Lack of agreement between thermodilution and electrical velocimetry cardiac output measurements

Objective: The modified algorithm for the non-invasive determination of cardiac output (CO) by electrical bioimpedance - electrical velocimetry (EV (R)) - has been reported to give reliable results in comparison with echocardiography and pulmonary arterial thermodilution (PA-TD) in patients either before or after cardiac surgery. The present study was designed to determine whether EV (R)-CO measurements reflect intraindividual changes in CO during cardiac surgery. Design: Prospective, observational study. Setting: Operating room (OR) and intensive care unit (ICU) of a university hospital. Patients: Twenty-nine patients undergoing elective cardiac surgery. Interventions: None. Measurements: CO was determined simultaneously by PA-TD and EV (R) after induction of anesthesia (t1) and 4.9 +/- 3.5 h after ICU admission (t2). Results: TD-CO was 3.9 +/- 1.4 and 5.4 +/- 1.1 l/min at t1 and t2 (p < 0.0001). EV (R)-CO was 4.3 +/- 1.1 and 4.9 +/- 1.5 l/min at t1 and t2 (p = 0.013). Bland-Altman analysis showed a bias of - 0.4 l/min and 0.4 l/min and a precision of 3.2 and 3.6 l/min (34.3% and 67.4%) at t1 and t2, respectively. Analysis of the individual pre- to postoperative changes in CO with both methods revealed bidirectional changes in n = 12 patients and unidirectional changes with a difference greater than 50% and less than 50% in n = 9 and n = 8 patients, respectively. Conclusions: The disagreement between PA-TD and EV (R)-CO measurements after anesthesia induction and after ICU admission, as well as the fact that thoracic bioimpedance did not adequately reflect pre- to postoperative changes in CO, questions the reliability of EV (R)- CO measurements in cardiac surgery patients and contrasts sharply with previous studies.